Measures of dispersion

• Examine variability in data

  Understand whether scores are similar or different
• Range

  • Simplest measure of dispersion
  • tells us how many numbers a distribution is spread
  • It is the difference between the highest and lowest score
• Evaluation of the range

  +Easy to caculate

  Takes into account exetreme scores

  -Ignores most scores
• Standard deviation

  • Tells us how far on average score is from the mean
  • Smaller the standard deviatio, the more scores are clustered around the mean
  • Larger the standard deviation is more spread out the scores
• Steps of SD

  • Caculate the mean score
  • Caculate the brackets (raw data minus mean)
  • Square scores in column B
  • Add up data in column C (The data squared) - add up squared differences
  • Divide total number of square differences by n-1
  • Square root